Field
The present invention relates to microelectromechanical systems and especially to a MEMS sensor and a semiconductor package including the MEMS sensor.
Description of the Related Art
One common application of MEMS technology is the design and manufacture of inertial sensing devices. In an inertial sensor, like a MEMS accelerometer, internal structures like proof masses, cantilevered beams and/or interdigitated comb fingers can be used to detect changes in motion of the sensor.
The measurement range of an accelerometer is the level of acceleration supported by the sensor's output signal specifications, typically specified in ±g. This is the greatest amount of acceleration the part can measure and accurately represent as an output. The accelerometers are classified as high-g, mid-g or low-g accelerometers depending on their highest output value specified by the full scale range.
Various types of MEMS sensors can be merged on a substrate along with integrated circuits (microelectronics) fabricated by separate process sequences. However, there is a constant need to reduce the size of the combination of sensors and circuits packaged together. For example, there are bi-axial and tri-axial accelerometers that detect inertial movements in two or three directions. Typically they have a separate MEMS element for detection of accelerations along each axis (x-,y-, and/or z-axis) of detection. The size and cost of such multi-element accelerometers can be excessive for many applications.
As another example, a modern car's airbag system uses acceleration sensors to determine the trigger point for release, and seat belt tensioners may be triggered by accelerometers. MEMS devices, such as accelerometers and gyroscopes, can also be used as sensors in Electronic Stability Control (ESC) technology to minimize the loss of car steering control in cars. In the future, ESC sensors are more and more integrated into the same location with the control unit and accelerometer of the airbag system. There is thus a need to integrate the low-g accelerometer and the gyroscope used as ESC sensors with the mid-g accelerometer of the airbag system to reduce component size and costs.
The mid-g accelerometer of the airbag system is often a 2-axis MEMS sensor that is sensitive to both longitudinal and transverse acceleration directions of a car. Conventionally such sensitivity has been achieved by mounting the whole mid-g accelerometer in a 45° angle on the printed circuit board the sensor is fabricated on. However, in integrated systems, the package size needs to be compact, so it is no longer feasible to mount the mid-g accelerometer in a 45° angle with respect to the ESC sensors.